1. Technical Field
The present invention relates to a delay circuit, a test apparatus, a storage medium, and a semiconductor chip. More particularly, the present invention relates to a delay circuit that can measure a delay amount of a delay element with high precision.
2. Related Art
Conventionally, there has been performed an initialization based on a delay amount generated by a delay element for delaying a signal with respect to a delay setting value set in the delay element. According to a conventional initialization, a loop path is formed on which a signal output from a delay element is again input into this delay element. A period for which the signal is transmitted through the loop path is measured, in order to measure a delay amount of the delay element.
For example, on the basis of a difference between a first loop period when a delay amount of a delay element is set to substantially zero and a second loop period when a predetermined delay setting value is set in the delay element, a delay amount with respect to this delay setting value is measured as disclosed, for example, in Japanese Patent Application Publication 2001-215261 and Japanese Patent Application Publication 2002-359289.
However, since the first loop period and the second loop period cannot be measured at the same time, a power supply voltage supplied to the delay element when measuring the first loop period may be different than a power supply voltage supplied to the delay element when measuring the second loop period. For example, a power supply voltage may vary due to a power source noise.
Since a delay amount of the loop path and the delay element varies when a power supply voltage varies, a measured delay amount has an error. For example, when a variation coefficient of a delay amount of the loop path and the delay element to the variation of the power supply voltage is 0.1%/mV, a result obtained by measuring the delay amount has an error of 0.1% if the power supply voltage has the variation of 1 mV.
Moreover, a delay amount on the loop path is much larger than a delay amount of the delay element. According to a conventional measuring method, since a difference between loop periods is generated by means of changing a delay setting value, a delay amount of the delay element has been measured from this difference. For this reason, the variation of the delay amount on the loop path caused by the variation of the power supply voltage results in a large error in a measurement result for the delay amount of the delay element.